1. Field of the Invention
The present invention relates to a method and related communications device for enhancing receiving efficiency of a multimedia broadcast multicast service (MBMS) in a wireless communications system, and more particularly to a method and related communications device for avoiding waste of processing resources and power in a user equipment (UE) of a wireless communications system.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. To enhance multimedia performance of the 3G mobile telecommunications system, the 3rd Generation Partnership Project (3GPP) provides a Multimedia Broadcast Multicast Service (MBMS), which is a point-to-multipoint bearer service established on an existing network architecture of the Universal Mobile Telecommunications System (UMTS). MBMS utilizes Internet Protocol (IP) packets as a medium, so that MBMS allows a single source entity to transmit data to multiple user entities simultaneously.
For improving performance of MBMS service broadcasting, a change request R2-071334 to a radio resource control (RRC) specification 3GPP TS 25.331 V7.3.0 (release-7) introduces a single frequency network (SFN) operation for MBMS transmission to reduce service interruption due to frequency switching during transmissions. In addition, a change request R2-071331 provides three kinds of network deployments of MBSFN (MBMS over a Single Frequency Network):
1. A time division duplex (TDD) carrier supports a mixed service of unicast and MBMS services of which some or all MBMS broadcast services are provided by SFN assigned with certain timeslots.
2. A TDD downlink-only carrier supports MBMS broadcast services via SFN.
3. A frequency division duplex (FDD) downlink-only carrier supports MBMS broadcast services via SFN.
According to specification developing principle, a newly developed specification should not impact on the previous version of the specification. To support MBSFN, the change request R2-071334 adds a new information element “MBSFN frequency list” in a system information block type 11 (SIB11) on a non-MBSFN carrier for notifying the UE of radio frequencies providing MBMS services transmitted on MBSFN. In addition, a dual receiver is employed in the UE, and thereby the UE needs to activate the second receiver of the dual receiver for receiving MBMS service notifications from the MBSFN carriers when the UE receives an MBMS service transmitted on a downlink-only carrier supporting the MBMS broadcast services via SFN. The change requests cause the following problems in such operation.
First, the change requests R2-071334 and R2-071331 do not disclose methods for distinguishing whether an MBMS service is transmitted on an MBSFN carrier or a non-MBSFN carrier. Thus, once an MBMS service is activated by an upper layer, the UE needs to monitor the MBMS service notifications from both the currently camped non-MBSFN carrier and the MBSFN carriers even though the MBMS service is actually transmitted on a non-MBSFN carrier. In this situation, monitoring the MBMS service notifications from the MBSFN carriers is needless for an MBMS service transmitted on a non-MBSFN carrier and therefore just causes unnecessary UE power consumption and degradation of receiving efficiency. More MBSFN carriers result in more power consumption.
Furthermore, when the UE receives an MBMS service transmitted on an MBSFN carrier, the UE needs to monitor the MBMS service notifications from multiple MBSFN carriers because more than one MBSFN carrier possibly is used for notification of the MBMS services. As a result, the UE has to switch between the MBSFN carriers regularly in order to get the up-to-date MBMS service notifications. Monitoring more MBSFN carriers causes more power consumption and degradation of receiving efficiency as well.